Gas generator for multi-stage air bag

ABSTRACT

A multistage type gas generator for an air bag, which has a simple structure and is easily manufactured and in which combustions of a gas generating means in a plurality of combustion chambers do not influence each other, is provided.  
     The present invention provides the multistage type gas generator for an air bag in which a plurality of combustion chambers accommodating gas generating agents are defined separately in a housing, and a plurality of the combustion chambers are provided to be aligned in the axial direction of the cylindrical housing.

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS

[0001] The present invention relates to a gas generator for an air bagwhich is suitably used in an inflating-type safety system of motorvehicles, and more particularly to a multistage type gas generator foran air bag which is provided with a plurality of combustion chambers andthat is preferable for manufacture and/or operation performance thereof.

PRIOR ART

[0002] An air bag system which is mounted on various kinds of vehiclesincluding automobiles, aims to hold the occupant by means of an air bag(a bag body) rapidly inflated by a gas when the vehicle collides at ahigh speed in order to prevent the occupant from crashing into a hardportion inside the vehicle such as a steering wheel, a windscreen due toan inertia and from being injured. This kind of an air bag apparatusgenerally comprises a sensor, a control unit, a pad module and the like,and the pad module comprises a module case, an air bag, a gas generatorand the like, and it is mounted to, for example, a steering wheel.

[0003] The gas generator among these members is constituted such that,when an igniting means is actuated by the impact, a gas generating meansis burnt to generate a gas with a high temperature and a high pressure,and thereby, the gas generated is ejected into the air bag (a bag body)to inflate the air bag and form a cushion absorbing the impact betweenthe steering wheel and the occupant.

[0004] Various kinds of such gas generators for an air bag have beenprovided conventionally, such as ones having different entire shapesoperating to a place to be mounted, or ones having different numbers ofcombustion chambers accommodating a gas generating means due to outputaspects of an operating gas for inflating an air bag.

[0005] Among these, a gas generator provided with a plurality ofcombustion chambers accommodating a gas generating agent have alreadybeen disclosed in JP-A 09-183359, JP-A 11-217055 or the like.

[0006] However, in these conventional gas generators, there is a roomfor improvement in manufacturing easiness or the like.

DISCLOSURE OF THE INVENTION

[0007] The present invention provides a multistage type gas generatorfor an air bag which can be easily manufactured. Also, the presentinvention provides a multistage type gas generator for an air bag inwhich a plurality of combustion chambers do not influence each others oncombustions of a gas generating means included in the respectivecombustion chambers and also, a gas generator which has a simplestructure and is easily assembled.

[0008] A multistage type gas generator for an air bag of the presentinvention comprises, in a cylindrical housing having a gas dischargingport, an igniting means to be activated by the activating signal and, ina plurality of combustion chambers defined separately in the cylindricalhousing, a gas generating means to be ignited and burnt by the ignitionmeans, in which a plurality of the combustion chambers are provided tobe aligned with each other in the axial direction of the cylindricalhousing

[0009] Also, a plurality of the combustion chambers are characterized bybeing provided adjacent to each other in the axial direction of thecylindrical housing.

[0010] Particularly, in the present invention, in case of a multistagetype gas generator for an air bag in which a plurality of the combustionchambers provided in the housing are arranged to be aligned to eachother in series and/or adjacent to each other in the axial direction ofthe cylindrical housing, and the respective combustion chambers aredefined not to be in communication with each other, and further anigniting means is provided in one combustion chambers side is employed,a plurality of the combustion chambers do not influence each other oncombustions of the gas generating means included in the combustionchambers, and thereby, for example, it is unnecessary to performcomplicated adjustment such as a breaking pressure of a gas dischargingport, or a size thereof, and an operation performance can be easilyadjusted. Further, assembling or mounting or charging of an innercylindrical member, an igniting means and a gas generating means can beconducted effectively and easily, and assembling of a gas generator isfacilitated. Also, when the igniting means is constituted to include anelectric ignition type igniter, a lead wire (or a connector) extendingfrom an actuation signal outputting means or the like can be coupledeasily.

[0011] Also, in the multistage type gas generator for an air bag of thepresent invention, it is desirable that a plurality of the combustionchambers provided in the cylindrical housing are separated from eachother by a partition wall formed in a plate shape, that the partitionwall is arranged on a combustion chamber in which the gas generatingmeans can be ignited the earliest among the adjacent combustionchambers, and that the partition wall abuts against an inner peripheralsurface of the cylindrical housing and/or an outer peripheral surface ofan inner cylindrical member. With this, the partition wall is pressedonto the inner surface of the housing or the like by combustion pressureof the gas generating means which is first ignited, so that the adjacentcombustion chambers can securely be separated, and movement of a fluidsuch as an operating gas between both the chambers can securely beblocked. Additionally, a seal can securely be achieved between theadjacent combustion chambers with a simple structure. For example, astructure supporting the partition wall which receives a combustionpressure of the gas generating means ignited the earliest can beprovided on an inner surface of the housing and at a position of thepartition wall. Also, the partition wall is formed by a circular portionand an annular portion formed integrally with a peripheral edge of thecircular portion, and the partition wall is designed to be recessedtowards the combustion chamber side storing the gas generating means tobe ignited the earliest. In this case, the annular portion of thepartition wall is pressed onto the inner surface of the housing and/orthe outer peripheral surface of the inner cylindrical member by acombustion pressure of the gas generating means.

[0012] Furthermore, in the multistage type gas generator for an air bagof the present invention, inner diameters of a plurality of combustionchambers defined separately in the housing can be made different, orinner diameters of a filter means arranged radially outside therespective combustion chambers can be made different. For example, thecylindrical housing is formed by a cylindrical diffuser shell with a tophaving a plurality of gas discharging ports provided in a peripheralwall and a closure shell closing a lower opening of the diffuser shell.Among a plurality of the combustion chambers defined separately in thehousing, the inner diameter of the combustion chamber nearest to theclosure shell is formed equally to or larger than those of the othercombustion chambers, and/or the inner diameter of the filter meansarranged radially outside the combustion chamber nearest to the closureshell can be formed equally to or larger than those of the filter meansarranged radially outside the other combustion chambers.

[0013] This is because, many gas generators are produced by sequentiallyassembling constituent members or the like with the diffuser shellturned upside down, and, with above formation, an inlet port at a timeof charging the gas generating means can be secured in abroad area, andcharging of the gas generating means can be performed easily andsecurely.

[0014] Further, it is desirable that, among the combustion chambersadjacent to each other in the cylindrical housing, an inner diameter ofthe combustion chamber storing the gas generating means to be ignitedlater is formed equally to or larger than that of the combustion chamberstoring the gas generating means capable of being ignited the earliest,and/or the inner diameter of the filter means arranged radially outsidethe combustion chamber storing the gas generating means to be ignitedlater is formed equally to or larger than that of the filter meansarranged radially outside the combustion chamber in which the gasgenerating means to be ignited the earliest.

[0015] The reason of the above is as follows: When the inner diametersof both the filter means are equal to each other, an amount of the gasgenerating agent in the combustion chamber accommodating the gasgenerating means which can be ignited at the later timing is generallysmall, and thereby, the combustion chamber is broadened radially (in adirection of a plan view) (namely, it becomes a thin and broadcombustion chamber), and the gas generating means in the combustionchamber has a difficulty in being ignited. However, when formed in theabove-described manner, the broadening of the inside of the combustionchamber in the radial direction (in the direction of the plan view) issuppressed, and the gas generating means in the combustion chamber canbe ignited easily.

[0016] Also, if a heat isolating member and/or a heat isolating spacewhich blocks conduction of a combustion heat of the gas generating meansin both the combustion chambers is provided between a plurality of thecombustion chambers separated in the cylindrical housing, a flametransfer between the both chambers can further securely be prevented.

[0017] Furthermore, a disk-shape retainer provided with an opening holein which an inner cylindrical member is fitted is arranged in thehousing, and the gas generator can easily be assembled by fixing thefilter means with the retainer, and a secure fixation can be achievedwith a simple structure.

[0018] According to the present invention, a multistage type gasgenerator for an air bag which has a simple structure and can easily bemanufactured is realized. Also, according to the present invention, amultistage gas generator for an air bag in which a gas generating meansrespectively included in a plurality of combustion chambers do notinfluence each other on combustions therein is realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a partially sectional view showing one embodiment of agas generator for an air bag of the present invention;

[0020]FIG. 2 is a horizontally sectional schematic view showing oneembodiment of a flame-direction controlling means; and

[0021]FIG. 3 is horizontally sectional schematic view showing anotherembodiment of a flame-direction controlling means.

EXPLANATION OF REFERENCE NUMERALS

[0022]1 diffuser shell

[0023]2 closure shell

[0024]3 housing

[0025]4(a, b) inner cylindrical member

[0026]5(a, b) filter means

[0027]6(a, b) gas generating agent

[0028]7(a, b) transfer charge

[0029]8(a, b) igniter

[0030]9(a, b) flame-transferring hole

[0031]10 partition wall

[0032]11(a, b) gas discharging port row

[0033]12(a, b) retainer

[0034]14(a, b) combustion chamber

[0035]60 wall portion

[0036] S space portion

PREFERRED EMBODIMENTS OF THE INVENTION

[0037] One embodiment of a gas generator for an air bag of the presentinvention will be explained with reference to the drawings. FIG. 1 is avertical sectional view showing one embodiment of a gas generator for anair bag of the present invention.

[0038] In the gas generator shown in this drawing, in a cylindricalhousing 3 having a gas discharging port 11, two inner cylindrical member4 a and 4 b, which stores igniting means (8 a and 8 b) in the innerspace, are disposed in parallel, and two filter means 5 a and 5 b formedannularly are disposed to face an inner surface of the housing 3. Acombustion chamber 14 formed between the two inner cylindrical members 4a and 4 b and the two filter means 5 a and 5 b are formed to be alignedin the axial direction of the cylindrical housing 3 and adjacent to eachother, and both the combustion chambers 14 a and 14 b are separated by apartition wall 10. Disk-shaped gas generating agents 6 a and 6 b areaccommodated in the respective combustion chambers 14 a and 14 b as agas generating means. Incidentally, only one of the inner cylindricalmembers 4 a and 4 b can be arranged. In this case, other igniting means(8 a and 8 b) may be arranged directly in the housing 3.

[0039] The cylindrical housing 3 consists of a cylindrical diffusershell 1 with a top and a closure shell 2 closing a lower end opening ofthe diffuser shell. In the diffuser shell 1, two gas discharging portrows 11 a and 11 b comprising a plurality of gas discharging ports 11aligned in a circumferential direction are formed at different positionsin the axial direction (namely, a vertical direction). Also in thediffuser shell 1, a bent portion 13 is formed between the two gasdischarging port rows 11 a and 11 b, and the inner diameter thereof isformed to be spread towards an opening end side (namely, the closureshell 2 side). The opening end of the diffuser shell 1 is formed in aflange shape, and a disk-shaped closure shell 2 is welded to theflange-shaped portion.

[0040] In this embodiment, regarding the two combustion chambers 14 aand 14 b defined separately in the housing 3, for the sake ofexplanation, a combustion chamber defined in the closure shell 2 side(namely, on the lower side in the drawing) is defined as a firstcombustion chamber 14 a and a combustion chamber defined on the otherend side (namely, on the upper side in the drawing) is defined as asecond combustion chamber 14 b. Also, the gas generating agentaccommodated in the first combustion chamber 14 a is defined as a firstgas generating agent 6 a, and the gas generating agent accommodated inthe second combustion chamber 14 b is defined as a second gas generatingagent 6 b. Accordingly, in this embodiment, between combustion chambersdefined, the first combustion chamber 14 a is provided nearer to theclosure shell 2.

[0041] Two inner cylindrical members 4 a and 4 b are arranged inparallel to each other inside the housing 3, and igniting meansincluding electric ignition type igniters 8 a and 8 b which respectivelyreceive electric actuation signals for actuation, and transfer charges 7a and 7 b which are to be ignited by actuations of the igniters areaccommodated in inner spaces of the respective inner cylindrical members4 a and 4 b. In both the inner cylindrical members 4 a and 4 b providedin parallel, the respective igniting means (8 a and 8 b) are arranged inthe closure 2 side, and they are positioned on the same plane.

[0042] Also, in peripheral walls of the inner cylindrical members 4 aand 4 b, a plurality of flame-transferring holes 9 aligned in thecircumferential direction. The flame-transferring holes 9 a and 9 bformed in the respective inner cylindrical members 4 a and 4 b are incommunication with different combustion chambers 14 a and 14 b in therespective inner cylindrical members. In this embodiment, theflame-transferring holes (first flame-transferring holes 9 a) formed inthe inner cylindrical member (hereinafter, referred to as a first innercylindrical member 4 a) arranged on the left side on the drawing are incommunication with the first combustion chamber 14 a, and theflame-transferring holes (second flame-transferring holes 9 b) formed inthe inner cylindrical member (hereinafter, referred to as a secondcylindrical member 4 b) arranged on the right side on the drawing are incommunication with the second combustion chamber 14 b.

[0043] In this embodiment, both the inner cylindrical members 4 a and 4b are arranged eccentrically in the cylindrical housing 3. When theinner cylindrical members 4 are arranged eccentrically in this manner,desirably, a flame-direction controlling means which controls directionsof flames ejected from either or all of the flame-transferring holes 9 aand 9 b. Such a flame-direction controlling means is formed in order tocontrol an ejecting direction of flames generated due to actuation of atleast the igniting means (8 a and 8 b), and, for example, like innercylindrical members 54 shown in FIGS. 2(a) and 2(b), it can be formed asa hollow container enclosing a portion of the igniting means generatingflames in which flames are generated and which has two or moreflame-transferring holes 59 for restricting a spouting direction (shownwith an arrow in the figures) of a flame in a desired direction. In thiscase, it is desirable that the ejecting direction of a flame controlledby the flame-direction controlling means (namely, the flame-transferringholes 59 formed partially in the inner cylindrical member 54) coincideswith a direction along an outer peripheral surface of the combustionchamber 14 (that is, a direction along an inner peripheral surface ofthe filter means 5). In FIGS. 2(a) and 2(b), the flame-directioncontrolling means is provided in either one of left and right innercylindrical members 54 on the drawings, but, of course, theflame-direction controlling means can be provided in both the innercylindrical members 54. Also, as shown in FIG. 3, as the flame-directioncontrolling means, a bow-shaped wall portion 60 is provided, so that theejecting direction of a flame generated by actuation of the ignitingmeans can be restricted. Further, the transfer charge shown in FIG. 1 isaccommodated in a container having openings only in a specificdirection, and with the container, the ejecting direction of a flame iscontrolled. In FIGS. 2 and 3, the same members as those shown in FIG. 1are designated with the same numerals, and explanation thereof will beomitted.

[0044] In FIG. 1, a partition wall 10 separating the first combustionchamber 14 a from the second combustion chamber 14 b comprises acircular portion 16 having opening holes 15 a and 15 b into which twoinner cylindrical members 4 a and 4 b are fitted, and an annular portion17 bending down from a peripheral edge of the circular portion 16 andformed integrally with the circular portion, and the annular portion isabutted on/is supported to a bent portion 13 of the diffuser shell 1 andarranged in the first combustion chamber 14 a side. In other words, theannular portion 17 of the partition wall 10 contacts an inner surface ofthe housing 3 in the first combustion chamber 14 a side. In this case,the partition wall 10 may abut against the inner cylindrical members 4 aand 4 b. When the first gas generating agent 6 a accommodated in thefirst combustion chamber 14 a is ignited/burnt, the partition wall 10existing in the first combustion chamber 14 a side is subjected to acombustion pressure and abut against the inner surface of the housing 3securely. Also, the partition wall 10 can be welded to the cylindricalhousing 3 and/or the inner cylindrical members 4 a and 4 b, or a stepcan be provided in the inner cylinder so that the partition wall isfitted thereon to be fixed, or a strut such as a supporting rod isarranged in either one of the combustion chambers. In such cases, evenwhen either of the gas generating agents 6 a and 6 b of the combustionchambers 14 a and 14 b is burnt firstly, the partition wall 10 cansecurely remain held/fixed. As compared with a case such that thepartition wall just abuts against them, the partition wall can beprevented from deforming or the like when the first gas generating agent6 a is ignited and burnt.

[0045] This partition wall not only defines the respective combustionchambers 14 a and 14 b but also it defines, in the axial direction ofthe housing, the inner space of the housing formed outside of the twocylindrical members 4 a and 4 b inside the housing. The innercylindrical members 4 a and 4 b penetrating the partition wall 10 arearranged to penetrate the combustion chamber 14. Incidentally, the innercylindrical member 4 may be arranged not to penetrate any combustionchamber.

[0046] The annular filter means 5 a and 5 b are disposed for therespective combustion chambers inside the inner space of the housing 3,which is defined by the partition wall 10, and also outwardly in theradial directions of the respective combustion chambers 14 a and 14 b soas to be opposite to the inner surface of the housing. The filter means5 may be formed by winding a metal wire mesh to be layered, oralternatively, it may be formed by winding an expanded metal to bemulti-layered. Besides, a member which can cool/purify an operating gasgenerated by combustion of the gas generating agent can be used as thefilter means.

[0047] In the present embodiment, the filter means 5 are different atthe respective combustion chambers 14 a and 14 b, and particularly, thefilter means 5 a and 5 b are different in their inner diameters. Inother words, the filter means (hereinafter, referred to as a firstfilter means 5 a) which is arranged radially outside the combustionchamber (hereinafter, referred to as a first combustion chamber 14 a)provided in the closure shell side has a larger inner diameter than thatof the filter means (hereinafter, referred to as a second filter means 5b) which is arranged radially outside the combustion chamber (that is,the second combustion chamber 14 b) provided far from the closure shell.Thereby, charging of the gas generating agent 6 into the combustionchamber provided inside the filter means 5 can easily be performed. Thisis to obtain a wide opening when assembling is performed with thediffuser shell turned upside-down. Also, as the second filter means 5 bhas a smaller inner diameter than that of the first filter means 5 a,with respect to the combustion chambers 14 provided inside therespective filter means, the second combustion chamber 14 b is formedradially smaller than the first combustion chamber 14 a. With thisdesign, the second gas generating agent 6 b can be burnt more easily.

[0048] The respective filter means 5 a and 5 b are supported byretainers 12 arranged in the respective combustion chambers 14 a and 14b. The retainer 12 comprises a circular portion 19 having opening holes18 a and 18 b in which two inner cylindrical members 4 a and 4 b arefitted, and an annular portion 20 formed integrally with the circularportion at a peripheral edge thereof. And outer peripheral surfaces ofthe annular portions 20 of the respective retainers 12 a and 12 b abutagainst inner peripheral surfaces of the respective filter means 5 a and5 b to support them.

[0049] In particular, in the gas generator shown in the presentembodiment, the second retainer 12 b arranged inside the secondcombustion chamber 14 b is disposed to secure a space portion S betweenthe second retainer and the partition wall 10 defining two combustionchambers. The space portion S can function as a heat-insulating spaceportion, which can block conduction of a combustion heat of the gasgenerating agent in either combustion chamber to the other combustionchamber side to the utmost. Also, instead of the heat insulating spaceor together with the heat insulating space, a heat-insulating memberformed with a member having at least heat insulating performance can bearranged between both the combustion chambers.

[0050] Incidentally, when the partition wall 10 separates the combustionchambers but it does not define a housing inner space formed outside ofthe two inner cylindrical members 4 a and 4 b inside the housing, asingle cylindrical filter means can be arranged oppositely to a housinginner surface.

[0051] Next, an operation of the gas generator shown in the figure willbe explained. By actuation of the first igniter 8 a included in thefirst igniting means, the first transfer charge 7 a positioned justabove is ignited and burnt, and a flame thereof ruptures a seal tapeclosing the flame-transferring holes 9 a formed in the first innercylindrical member 4 a to eject into the first combustion chambers 14 a,thereby igniting and burning the first gas generating agent 6 a. Thefirst gas generating agent 6 a burns so that an operating gas forinflating an air bag is generated and the gas passes through the firstfilter means 5 a to be discharged from the first gas discharging portrow 11 a.

[0052] Meanwhile, equally when the second igniter 8 b included in thesecond igniting means is actuated, the second transfer charge 7 b isignited and burnt, and a flame thereof ejects from theflame-transferring holes 9 b formed in the second inner cylindricalmember 4 b into the second combustion chamber 14 b to ignite and burnthe second gas generating agent 6 b and generate an operating gas, sothat the gas passes through the second filter means 5 b to be dischargedfrom the second gas discharging port row 11 b.

[0053] Actuation timings of the first igniter 8 a and the second igniter8 b are adjusted properly in order to obtain an optimal output patternof a operating gas required at a time of actuation of the gas generator.For example, the actuation timing is adjusted such that the firstigniter 8 a and the second igniter 8 b simultaneously are actuated,thereby burning the gas generating agents 6 a and 6 b accommodated inthe two combustion chambers simultaneously, or such that, the secondigniter 8 b is actuated, slightly after the first igniter 8 a isactuated, thereby differentiating combustion start timings of the gasgenerating agents accommodated in the respective combustion chambers.

[0054] In particular, when the first igniter 8 a is actuated slightlyearlier than the second igniter 8 b, the second gas generating agent 6 bis left unignited while the first gas generating agent 6 a is burnt togenerate a operating gas. Even in such a case, it is desirable that theignition start timing of the second gas generating agent 6 b is adjustedexclusively by the second igniting means. In the gas generator shown inthe present embodiment, the first combustion chamber 14 a and the secondcombustion chamber 14 b are separated by the partition wall 10, thefirst filter means 5 a is not the same as the second filter means 5 ba,and the first filter means is arranged in a space defined separatelyfrom the second filter means 5 b. Therefore, a operating gas generatedby combustion of the first gas generating agent 6 a is prevented fromflowing into the second combustion chamber 14 b. Also, theheat-insulating space is secured between the first combustion chamber l4a and the second combustion chamber 14 b, so that the combustion heat ofthe first gas generating agent 6 a is prevented from conducting to thesecond combustion chamber 14 b via the partition wall 10 or the like.Accordingly, in the gas generator shown in the present embodiment, evenwhen gas generating agents in the respective combustion chambers areignited at different timings, ignition timings of the respective gasgenerating agents can be adjusted exclusively at actuation timings ofthe respective igniting means.

[0055] By adjusting the activation timings of the respective ignitingmeans (or the respective igniters), the output aspect (operationperformance) of the gas generator can arbitrarily be adjusted. Invarious situations such as a speed of a vehicle at a time of collision,an environmental temperature, or the like, a development of an air bagcan be set most properly when the gas generator is applied to an air bagapparatus described later. Incidentally, gas generating agents withdifferent shapes (for example, a single-perforated gas generating agentand a porous gas generating agent) can be used for the respective firstand second combustion chambers. Also, amounts of the gas generatingagents accommodated in the first and second combustion chamber can beadjusted properly. The shape, size, composition, composition ratio,amount and the like of the gas generating agent can, of course, bemodified properly in order to obtain a desired output aspect.

1. A multistage type gas generator for an air bag comprising, in acylindrical housing having a gas discharging port, an igniting means tobe actuated by an actuation signal and, in a plurality of combustionchambers defined separately in the cylindrical housing, a gas generatingmeans to be ignited and burnt by the igniting means, wherein a pluralityof the combustion chambers are provided to be aligned in the axialdirection of the cylindrical housing.
 2. A multistage type gas generatorfor an air bag comprising, in a cylindrical housing having a gasdischarging port, an igniting means to be actuated by an actuationsignal and, in a plurality of combustion chambers defined separately inthe cylindrical housing, a gas generating means to be ignited and burntby the igniting means, wherein a plurality of the combustion chambersare provided adjacent to each other in the axial direction of thecylindrical housing.
 3. A multistage type gas generator for an air bagaccording to claim 1 or 2, wherein at least one inner cylindrical memberprovided on its peripheral wall with a plurality of flame-transferringholes is arranged in the cylindrical housing, and the igniting means isaccommodated in an inner space of the inner cylindrical member.
 4. Amultistage type gas generator for an air bag according to claim 3,wherein the inner cylindrical member is arranged to penetrate, in theaxial direction of the cylindrical housing, either one of a plurality ofthe combustion chambers defined separately in the cylindrical housing.5. A multistage type gas generator for an air bag according to claim 3or 4, wherein the inner space of the inner cylindrical member is incommunication with either of a plurality of the combustion chambersdefined separately in the cylindrical housing.
 6. A multistage type gasgenerator for an air bag according to any one of claims 3 to 5, whereineither of the inner cylindrical members arranged in the housing isarranged eccentrically in the housing, and an ejecting direction of aflame ejected from the flame-transferring holes of the inner cylindricalmember arranged eccentrically is controlled by a flame-directioncontrolling means.
 7. A multistage type gas generator for an air bagaccording to any one of claims 1 to 6, wherein a cylindrical filtermeans for purifying and/or cooling an operating gas generated bycombustion of the gas generating means are arranged in the cylindricalhousing, and the filter means are arranged radially in the operatingoutside of the combustion chambers separated in the cylindrical housing,respectively.
 8. A multistage type gas generator for an air bagaccording to claim 7, wherein the cylindrical housing comprises acylindrical diffuser shell with a top provided on a peripheral wall witha plurality of gas discharging ports and a closure shell which closes alower opening of the diffuser shell, and among a plurality ofcylindrical filter means arranged radially outside the respectivecombustion chambers, the inner diameter of the cylindrical filter meansdisposed in the closure shell side is equal to or larger than that ofthe filter means arranged far from the closure shell.
 9. A multistagetype gas generator for an air bag according to any one of claims 1 to 8,wherein the cylindrical housing comprises a cylindrical diffuser shellwith a top provided on a peripheral wall with a plurality of gasdischarging ports and a closure shell which closes a lower opening ofthe diffuser shell, and the inner diameter of the combustion chamberprovided nearest to the closure shell side in the cylindrical housing isequal to or larger than that of other combustion chamber.
 10. Amultistage type gas generator for an air bag according to any one ofclaims 1 to 9, wherein a heat insulating member and/or a heat insulatingspace which blocks conduction of a combustion heat of the gas generatingmeans between the combustion chambers is provided between a plurality ofthe combustion chambers which are defined separately in the cylindricalhousing.
 11. A multistage type gas generator for an air bag according toany one of claims 1 to 10, wherein the igniting means is provided thesame number as that of the combustion chambers defined separately in thecylindrical housing, and any of the igniting means are arranged on thesame side inside the cylindrical housing.
 12. A multistage type gasgenerator for an air bag according to any one of claims 1 to 11, whereinthe igniting means is provided the same number as that of the combustionchambers defined separately in the cylindrical housing, and the ignitingmeans are arranged on the same plane in the cylindrical housing.
 13. Amultistage type gas generator for an air bag according to any one ofclaims 1 to 12, wherein the cylindrical housing comprises a cylindricaldiffuser shell with a top provided on a peripheral wall with a pluralityof gas discharging ports and a closure shell which closes a loweropening of the diffuser shell, the igniting means is provided the samenumber as that of the combustion chambers defined separately in thecylindrical housing, and any of the respective igniting means arearranged on the closure shell side.
 14. A multistage type gas generatorfor an air bag according to any one of claims 1 to 13, wherein aplurality of the combustion chambers defined separately in thecylindrical housing are separated from each other by a partition wallformed in a plate shape.
 15. A multistage type gas generator for an airbag according to claim 14, wherein the partition wall is arranged on thecombustion chamber storing the gas generating means capable of beingignited the earliest, and the partition wall abuts against an innerperipheral surface of the cylindrical housing and/or an outer peripheralsurface of the inner cylindrical member among the combustion chambersadjacent to each other.
 16. A multistage type gas generator for an airbag according to claim 14 or 15, wherein the partition wall is welded tothe cylindrical housing and/or the inner cylindrical member arranged inthe housing.
 17. A multistage type gas generator for an air bagcomprising, in a cylindrical housing having a gas discharging port, anigniting means to be actuated by an actuation signal and, in a pluralityof combustion chambers defined separately in the cylindrical housing, agas generating means to be ignited and burnt by the igniting means,wherein at least one inner cylindrical member provided on a peripheralwall with a plurality of flame-transferring holes is arranged in thecylindrical housing, and the igniting means is accommodated in an innerspace of the inner cylindrical member.
 18. A multistage type gasgenerator for an air bag according to claim 17, wherein the innercylindrical member is arranged in the axial direction of the cylindricalhousing to penetrate either of a plurality of the combustion chambersdefined separately in the cylindrical housing.
 19. A multistage type gasgenerator for an air bag according to claim 17 or 18, wherein the innerspace of the inner cylindrical member is in communication with either ofa plurality of the combustion chambers defined separately in thecylindrical housing.
 20. A multistage type gas generator for an air bagaccording to any one of claims 17 to 19, wherein either of the innercylindrical members arranged in the housing is arranged eccentrically inthe housing, and an ejecting direction of a flame ejected from theflame-transferring holes of the inner cylindrical member arrangedeccentrically is controlled by a flame-direction controlling means. 21.A multistage type gas generator for an air bag according to any one ofclaims 17 to 20, wherein a cylindrical filter means for purifying and/orcooling an operating gas generated by combustion of the gas generatingmeans are arranged in the cylindrical housing, and the filter means arearranged radially in the corresponding outside of the combustionchambers separated in the cylindrical housing, respectively chamber. 22.A multistage type gas generator for an air bag according to claim 21,wherein the cylindrical housing comprises a cylindrical diffuser shellwith a top provided on a peripheral wall with a plurality of gasdischarging ports and a closure shell which closes a lower opening ofthe diffuser shell, and among a plurality of cylindrical filter meansarranged radially outside the respective combustion chambers, the innerdiameter of the cylindrical filter means arranged in the closure shellside is equal to or larger than that of the cylindrical filter meansarranged far from the closure shell.
 23. A multistage type gas generatorfor an air bag according to any one of claims 17 to 22, wherein thecylindrical housing comprises a cylindrical diffuser shell with a topprovided on a peripheral wall with a plurality of gas discharging portsand a closure shell which closes a lower opening of the diffuser shell,and the inner diameter of the combustion chamber provided nearest to theclosure shell in the cylindrical housing is equal to or larger than thatof other combustion chamber.
 24. A multistage type gas generator for anair bag according to any one of claims 17 to 23, wherein a heatinsulating member and/or a heat insulating space which blocks conductionof a combustion heat of the gas generating means between the combustionchambers is provided between a plurality of the combustion chamberswhich are defined separately in the cylindrical housing.
 25. Amultistage type gas generator for an air bag according to any one ofclaims 17 to 24, wherein the igniting means is provided the same numberas that of the combustion chambers defined separately in the cylindricalhousing, and any of the respective igniting means are arranged on thesame side in the cylindrical housing.
 26. A multistage type gasgenerator for an air bag according to any one of claims 17 to 25,wherein the igniting means is provided the same number as that of thecombustion chambers defined separately in the cylindrical housing, andthe respective igniting means are arranged on the same plane in thecylindrical housing.
 27. A multistage type gas generator for an air bagaccording to any one of claims 17 to 26, wherein the cylindrical housingcomprises a cylindrical diffuser shell with a top provided on aperipheral wall with a plurality of gas discharging ports and a closureshell which closes a lower opening of the diffuser shell, the ignitingmeans is provided the same number as that of the combustion chambersdefined separately in the cylindrical housing, and any of the respectiveigniting means are arranged in the closure shell side.
 28. A multistagetype gas generator for an air bag according to any one of claims 17 to27, wherein a plurality of the combustion chambers defined separately inthe cylindrical housing are separated from each other by a partitionwall formed in a plate shape.
 29. A multistage type gas generator for anair bag according to claim 28, wherein the partition wall is arrangednear the combustion chamber, among the combustion chambers adjacent toeach other, storing the gas generating means capable of being ignitedthe earliest, and the partition wall abuts against an inner peripheralsurface of the cylindrical housing and/or an outer peripheral surface ofthe inner cylindrical member.
 30. A multistage type gas generator for anair bag according to claim 28 or 29, wherein the partition wall iswelded to the cylindrical housing and/or the inner cylindrical memberarranged in the housing.
 31. A multistage type gas generator for an airbag comprising, in a cylindrical housing having a gas discharging port,an igniting means to be actuated by an actuation signal and, in aplurality of combustion chambers defined separately in the cylindricalhousing, a gas generating means to be ignited and burnt by the ignitingmeans, wherein a cylindrical filter means for purifying and/or coolingan operating gas generated by combustion of the gas generating means arearranged in the cylindrical housing, and the filter means are arrangedradially in the corresponding outside of the combustion chambersseparated in the cylindrical housing, respectively.
 32. A multistagetype gas generator for an air bag according to claim 31, wherein thecylindrical housing comprises a cylindrical diffuser shell with a topprovided on a peripheral wall with a plurality of gas discharging portsand a closure shell which closes a lower opening of the diffuser shell,and among a plurality of cylindrical filter means arranged radiallyoutside the respective combustion chambers, the inner diameter of thecylindrical filter means arranged in the closure shell side is equal toor larger than that of the filter means arranged far from the closureshell.
 33. A multistage type gas generator for an air bag according toclaim 31 or 32, wherein the cylindrical housing comprises a cylindricaldiffuser shell with a top provided on a peripheral wall with a pluralityof gas discharging ports and a closure shell which closes a loweropening of the diffuser shell, and the inner diameter of the combustionchamber provided nearest to the closure shell in the cylindrical housingis equal to or larger than that of other combustion chamber.
 34. Amultistage type gas generator for an air bag according to any one ofclaims 31 to 33, wherein a heat insulating member and/or a heatinsulating space which blocks conduction of a combustion heat of the gasgenerating means between the combustion chamber is provided between aplurality of the combustion chambers which are defined separately in thecylindrical housing.
 35. A multistage type gas generator for an air bagaccording to any one of claims 31 to 34, wherein the igniting means isprovided the same number as that of the combustion chambers definedseparately in the cylindrical housing, and any of the respectiveigniting means are arranged on the same side in the cylindrical housing.36. A multistage type gas generator for an air bag according to any oneof claims 31 to 35, wherein the igniting means is provided the samenumber as that of the combustion chambers defined separately in thecylindrical housing, and the respective igniting means are arranged onthe same plane in the cylindrical housing.
 37. A multistage type gasgenerator for an air bag according to any one of claims 31 to 36,wherein the cylindrical housing comprises a cylindrical diffuser shellwith a top provided on a peripheral wall with a plurality of gasdischarging ports and a closure shell which closes a lower opening ofthe diffuser shell, the igniting means is provided the same number asthat of the combustion chambers defined separately in the cylindricalhousing, and any of the respective igniting means are arranged in theclosure shell side.
 38. A multistage type gas generator for an air bagaccording to any one of claims 31 to 37, wherein a plurality of thecombustion chambers defined separately in the cylindrical housing areseparated from each other by a partition wall formed in a plate shape.39. A multistage type gas generator for an air bag according to claim38, wherein the partition wall is arranged on the combustion chamberstoring the gas generating means capable of being ignited the earliest,and the partition wall abuts against an inner peripheral surface of thecylindrical housing and/or an outer peripheral surface of the innercylindrical member among the combustion chambers adjacent to each other.40. A multistage type gas generator for an air bag according to claim 38or 39, wherein the partition wall is welded to the cylindrical housingand/or the inner cylindrical member arranged in the housing.
 41. Amultistage type gas generator for an air bag comprising, in acylindrical housing having a gas discharging port, an igniting means tobe actuated by an actuation signal and, in a plurality of combustionchambers defined separately in the cylindrical housing, a gas generatingmeans to be ignited and burnt by the igniting means, wherein thecylindrical housing comprises a cylindrical diffuser shell with a topprovided on a peripheral wall with a plurality of gas discharging portsand a closure shell which closes a lower opening of the diffuser shell,and the inner diameter of the combustion chamber provided nearest to theclosure shell in the cylindrical housing is equal to or larger than thatof other combustion chamber.
 42. A multistage type gas generator for anair bag according to claim 41, wherein a heat insulating member and/or aheat insulating space which blocks conduction of a combustion heat ofthe gas generating means between the combustion chambers is providedbetween a plurality of the combustion chambers which are definedseparately in the cylindrical housing.
 43. A multistage type gasgenerator for an air bag according to any one of claims 41 or 42,wherein the igniting means is provided the same number as that of thecombustion chambers defined separately in the cylindrical housing, andany of the respective igniting means are arranged on the same side inthe cylindrical housing.
 44. A multistage type gas generator for an airbag according to any one of claims 41 to 43, wherein the igniting meansis provided the same number as that of the combustion chambers definedseparately in the cylindrical housing, and the respective igniting meansare arranged on the same plane in the cylindrical housing.
 45. Amultistage type gas generator for an air bag according to any one ofclaims 41 to 44, wherein the cylindrical housing comprises a cylindricaldiffuser shell with a top provided on a peripheral wall with a pluralityof gas discharging ports and a closure shell which closes a loweropening of the diffuser shell, the igniting means is provided the samenumber as that of the combustion chambers defined separately in thecylindrical housing, and any of the respective igniting means arearranged in the closure shell side.
 46. A multistage type gas generatorfor an air bag according to any one of claims 41 to 45, wherein aplurality of the combustion chambers defined separately in thecylindrical housing are separated from each other by a partition wallformed in a plate shape.
 47. A multistage type gas generator for an airbag according to claim 46, wherein the partition wall is arranged on thecombustion chamber storing the gas generating means capable of beingignited the earliest, and the partition wall abuts against an innerperipheral surface of the cylindrical housing and/or an outer peripheralsurface of the inner cylindrical member among the combustion chambersadjacent to each other.
 48. A multistage type gas generator for an airbag according to claim 46 or 47, wherein the partition wall is welded tothe cylindrical housing and/or the inner cylindrical member arranged inthe housing.
 49. A multistage type gas generator for an air bagcomprising, in a cylindrical housing having a gas discharging port, anigniting means to be actuated by an actuation signal and, in a pluralityof combustion chambers defined separately in the cylindrical housing, agas generating means to be ignited and burnt by the igniting means,wherein a heat insulating member and/or a heat insulating space whichblocks conduction of a combustion heat of the gas generating meansbetween the combustion chambers is provided between a plurality of thecombustion chambers which are defined separately in the cylindricalhousing.
 50. A multistage type gas generator for an air bag according toclaim 49, wherein the igniting means is provided the same number as thatof the combustion chambers defined separately in the cylindricalhousing, and any of the respective igniting means are arranged on thesame side in the cylindrical housing.
 51. A multistage type gasgenerator for an air bag according to claim 49 or 50, wherein theigniting means is provided the same number as that of the combustionchambers defined separately in the cylindrical housing, and therespective igniting means are arranged on the same plane in thecylindrical housing.
 52. A multistage type gas generator for an air bagaccording to any one of claims 49 to 51, wherein the cylindrical housingcomprises a cylindrical diffuser shell with a top provided on aperipheral wall with a plurality of gas discharging ports and a closureshell which closes a lower opening of the diffuser shell, the ignitingmeans is provided the same number as that of the combustion chambersdefined separately in the cylindrical housing, and any of the respectiveigniting means are arranged in the closure shell side.
 53. A multistagetype gas generator for an air bag according to any one of claims 49 to52, wherein a plurality of the combustion chambers defined separately inthe cylindrical housing are separated from each other by a partitionwall formed in a plate shape.
 54. A multistage type gas generator for anair bag according to claim 53, wherein the partition wall is arranged onthe combustion chamber storing the gas generating means capable of beingignited the earliest and the partition wall abuts against an innerperipheral surface of the cylindrical housing and/or an outer peripheralsurface of the inner cylindrical member among the combustion chambersadjacent to each other.
 55. A multistage type gas generator for an airbag according to claim 53 or 54, wherein the partition wall is welded tothe cylindrical housing and/or the inner cylindrical member arranged inthe housing.
 56. A multistage type gas generator for an air bagcomprising, in a cylindrical housing having a gas discharging port, anigniting means to be actuated by an actuation signal and, in a pluralityof combustion chambers defined separately in the cylindrical housing, agas generating means to be ignited and burnt by the igniting means,wherein the igniting means is provided the same number as that of thecombustion chambers defined separately in the cylindrical housing, andany of the respective igniting means are arranged on the same side inthe cylindrical housing.
 57. A multistage type gas generator for an airbag comprising, in a cylindrical housing having a gas discharging port,an igniting means to be actuated by an actuation signal and, in aplurality of combustion chambers defined separately in the cylindricalhousing, a gas generating means to be ignited and burnt by the ignitingmeans, wherein the igniting means is provided the same number as that ofthe combustion chambers defined separately in the cylindrical housing,and the respective igniting means are arranged on the same plane in thecylindrical housing.
 58. A multistage type gas generator for an air bagcomprising, in a cylindrical housing having a gas discharging port, anigniting means to be actuated by an actuation signal and, in a pluralityof combustion chambers defined separately in the cylindrical housing, agas generating means to be ignited and burnt by the igniting means,wherein the cylindrical housing comprises a cylindrical diffuser shellwith a top provided on a peripheral wall with a plurality of gasdischarging ports and a closure shell which closes a lower opening ofthe diffuser shell, and the igniting means is provided the same numberas that of the combustion chambers defined separately in the cylindricalhousing, and any of the respective igniting means are arranged in theclosure shell side.
 59. A multistage type gas generator for an air bagaccording to any one of claims 56 to 58, wherein a plurality of thecombustion chambers defined separately in the cylindrical housing areseparated from each other by a partition wall formed in a plate shape.60. A multistage type gas generator for an air bag according to claim59, wherein the partition wall is arranged on the combustion chamberstoring the gas generating means capable of being ignited the earliest,and the partition wall abuts against an inner peripheral surface of thecylindrical housing and/or an outer peripheral surface of the innercylindrical member among the combustion chambers adjacent to each other.61. A multistage type gas generator for an air bag according to claim 59or 60, wherein the partition wall is welded to the cylindrical housingand/or the inner cylindrical member arranged in the housing.
 62. Amultistage type gas generator for an air bag comprising, in acylindrical housing having a gas discharging port, an igniting means tobe actuated by an actuation signal and, in a plurality of combustionchambers defined separately in the cylindrical housing, a gas generatingmeans to be ignited and burnt by the igniting means, wherein a pluralityof the combustion chambers defined separately in the cylindrical housingare separated from each other by a partition wall formed in a plateshape.
 63. A multistage type gas generator for an air bag according toclaim 62, wherein the partition wall is arranged on the combustionchamber storing the gas generating means capable of being ignited theearliest, and the partition wall abuts against an inner peripheralsurface of the cylindrical housing and/or an outer peripheral surface ofthe inner cylindrical member among the combustion chambers adjacent toeach other.
 64. A multistage type gas generator for an air bag accordingto claim 62 or 63, wherein the partition wall is welded to thecylindrical housing and/or the inner cylindrical member arranged in thehousing.
 65. A multistage type gas generator for an air bag according toany one of claims 1 to 64, wherein the cylindrical housing comprises acylindrical diffuser shell with a top provided on a peripheral wall witha plurality of gas discharging ports and a closure shell which closes alower opening of the diffuser shell, and two combustion chambers aredefined separately in the cylindrical housing, and the two combustionchambers are arranged to be aligned in the axial direction of thecylindrical housing and adjacent to each other.